The hydroformylation of ethylenically unsaturated compounds, i.e. the catalytic addition of carbon monoxide and hydrogen to such compounds to produce aldehydes and/or alcohols is of great industrial importance. Aldehydes, in particular linear (i.e., straight-chain) aldehydes, are very useful intermediates in industrial practice because of their terminal carbonyl group. They can, for instance, be readily reduced to the corresponding primary alcohols and oxidized to the corresponding carboxylic acids. The aldehydes also undergo addition and/or condensation reactions with a variety of chemicals such as hydrogen cyanide, alcohols, nitroparaffins as well as condensation reactions with themselves and other carbonyl-containing compounds. They can also be reacted with ammonia and derivatives thereof such as primary amines.
Much effort has been devoted over the years to the development of better catalytic systems for hydroformylation reactions, especially with the objective to improve the ratio of linear to branched molcules in a product prepared from a linear starting material. Linearity of the carbon chain in the product molecule has a positive influence on properties such as biodegradability, which is of great importance in various applications wherein aldehydes and/or alcohols are used as intermediates or starting materials, and particularly in application wherein the hydroformylation product is used in the preparation of surfactant compounds.
Since it is known that the classical cobalt carbonyl catalyst system for hydroformylation produces a large amount of branched chain products, more advanced systems have been suggested comprising organophosphorus compounds, in particular tertiary phosphines or phosphites as ligands.
Not only ligands have been suggested as promoters and/or stabilizers for hydroformylation catalysts but also certain metal halides are recognized for this service. For instance, it is known that Group IVA metal halides, in particular tin(II)-halides, preferably also containing a quarternary ammonium halide, can also be applied to improve the linear/branched product ratio, especially when platinum is used as the main catalyst.
However, the use of Group IVA halides has the intrinsic drawback that normally a rather large excess of such compound is required which, makes the work-up procedure for recovery of product and recovery and recycle of starting material and catalyst very unattractive. Moreover, it appears that high linear/branched product ratios can only be obtained at the expense of an increasing amount of alkanes being co-produced. It is therefore very desirable to develop a hydroformylation catalyst, which matches the activity (e.g., reaction rate) of the cobalt-carbonyl based catalyst, while maintaining a high linear/branched product ratio with a minimal coproduction of undesired alkanes.